CLN5 disease
CLN5 disease is an inherited neurodegenerative disorder characterized by developmental regression, seizures, and motor decline, typically appearing in childhood.
Overview
CLN5 disease is an inherited disorder that primarily affects the nervous system. It belongs to a group of conditions known as neuronal ceroid lipofuscinoses (NCLs), or Batten disease. These disorders are distinguished by their specific genetic cause and result in progressive decline in vision, movement, and cognitive function.
Symptoms
Symptoms typically appear around age 5, though they can manifest anytime between childhood and early adulthood. Common features include:
- Developmental regression (loss of previously acquired motor skills).
- Recurrent seizures, specifically myoclonic epilepsy (uncontrollable muscle jerks).
- Ataxia (difficulty coordinating movements).
- Vision loss and speech problems.
- Decline in intellectual function.
Causes
The condition is caused by mutations in the CLN5 gene. This gene provides instructions for a protein that functions within lysosomes—cell compartments responsible for digesting and recycling molecules. When the CLN5 protein is dysfunctional, damaged or unneeded proteins accumulate within cells, leading to the widespread loss of nerve cells.
- Childhood onset: Mutations often prevent the protein from reaching the lysosomes, leading to severe, early-onset symptoms.
- Adolescent/Adult onset: Mutations may result in a protein with reduced function that persists for a short time, causing a slower accumulation of cellular waste and later symptom onset.
Inheritance
CLN5 disease is inherited in an autosomal recessive pattern. This means both copies of the CLN5 gene in each cell have mutations. Parents of an affected individual each carry one copy of the mutated gene but typically do not show signs of the condition.
Frequency
While originally thought to affect only the Finnish population, research shows CLN5 disease occurs worldwide. In Finland, the incidence is approximately 1 in 12,500 individuals. Collectively, all forms of NCL affect an estimated 1 in 100,000 people globally.